1. Field of the Invention
The present invention relates to a resin-diamagnetic material composite structure, and particularly to a resin-diamagnetic material composite structure that is useful as a heat dissipating member of a semiconductor device.
2. Description of the Related Art
As components that assume the effective utilization of energy, for example, there are a power element having a function of controlling electric power of a power supply, and a power module including the power element incorporated therein. Examples of important elements in the development of the power element include a semiconductor material that constitutes the power element. In the power element, it is proposed that materials such as GaN capable of coping with higher frequency and SIC having higher voltage resistance are used in place of conventional Si-based materials, and these materials are put into practical use.
When these materials are used, it is required to efficiently disperse heat generated from a power element to the surrounding environment. Thus, a substrate on which a power element is mounted is formed of a material having high heat dissipation, or a radiating plate or a radiating fin (collectively referred to as a “radiating member”) is provided adjacent to a substrate or a power element.
When a substrate is formed of a material (for example, metal) having high heat dissipation (thermal conductivity), the substrate often has electrical conductivity together with thermal conductivity. Therefore, in order to ensure insulation properties on a surface of a substrate, an insulating resin layer (layer of an insulating material) is disposed on a surface of a substrate, or a substrate is formed using a material prepared by kneading a resin having insulation properties with a material having high thermal conductivity.
As a heat dissipating plate, for example, a plate made of a metallic material such as copper (Cu) (metal plate) is used. The metallic material commonly has conductivity. For this reason, when a metal plate (radiating plate) is made adjacent directly to a substrate or a power element, electric continuity is generated, exerting an adverse influence on an operation of the power element or the power module. Therefore, the metal plate (radiating plate) is used in a state of being adjacent to a substrate or a power element via a layer made of an insulating material.
In other words, it is necessary for either a heat dissipating substrate or a radiating plate of a power module to use an insulating material (specifically, a resin). Regarding the heat dissipating substrate or radiating plate including a layer made of an insulating material, heat dissipation may be inhibited by the layer made of an insulating material, resulting in deterioration of heat dissipation characteristics. In a substrate in which a resin is mixed with a material having high thermal conductivity, the material having high thermal conductivity may be sometimes bonded in the resin to form conduction paths, and thus failing to ensure desired insulation properties.
These inconveniences may be avoided by an improvement in heat dissipation characteristics by using a material having higher thermal conductivity thereby to compensate deterioration of heat dissipation characteristics by use of an insulating resin. An attention is paid on graphite as the material having higher thermal conductivity than that of copper (Cu), and it is proposed to use the graphite for heat dissipation (see, for example, JP-A-2006-165153).
FIG. 6 is a partial cross-sectional view of a thermal conductive sheet disclosed in JP-A-2006-165153. As shown in FIG. 6, JP-A-2006-165153 discloses that a thermal conductive sheet 1 is configured that a plurality of small pieces 6 of a graphite sheet are mixed in an insulating sheet 5 made of a resin. JP-A-2006-165153 discloses that, with such a configuration, individual small pieces of a graphite sheet are independently disposed in an insulating sheet, ensuring electrical insulation properties while making use of high thermal conductivity possessed by the graphite sheet.